This invention relates generally to an electrophotographic copying device, and more particularly, a blade controller assembly used therein to remove particles adhering to the imaging surface (i.e. photoreceptor or photoconductor).
In an electrophotographic application such as xerography, a charge retentive surface is electrostatically charged, and exposed to a light pattern of an original image to be reproduced to selectively discharge the surface in accordance therewith. The resulting pattern of charged and discharged areas on that surface form an electrostatic charge pattern (an electrostatic latent image) conforming to the original image. The latent image is developed by contacting it with a finely divided electrostatically attractable powder referred to as "toner". Toner is held on the image areas by the electrostatic charge on the surface. Thus, a toner image is produced in conformity with a light image of the original being reproduced. The toner image may then be transferred to a substrate (e.g., paper), and the image affixed thereto to form a permanent record of the image to be reproduced. Subsequent to development, excess toner left on the charge retentive surface is cleaned from the surface. The process is well known, and useful for light lens copying from an original, and copying/printing applications from electronically generated or stored originals, where a charge surface may be imagewise discharged in a variety of ways. Ion projection devices, where a charge is imagewise deposited on a charge retentive substrate, operate similarly.
In a reproduction process of the type as described above, it is inevitable that some residual toner will remain on the photoconductive surface after the toner image has been transferred to the sheet of support material (e.g. paper). It has been found that with such a process that the forces holding some of the toner particles to the imaging surface are stronger than the transfer forces and, therefore, some of the particles remain on the surface after transfer of the toner image. In addition to the residual toner, other particles, such as paper debris (i.e. Kaolin, fibers, clay), additives and plastic, are left behind on the surface after image transfer. (Hereinafter, the term "residual particles" encompasses residual toner and other residual debris remaining after image transfer.) The residual particles adhere firmly to the surface and must be removed prior to the next copying cycle to avoid its interfering with recording a new latent image thereon.
Various methods and apparatus may be used for removing residual particles from the photoconductive imaging surface. One such method and/or apparatus is the use of a cleaning blade. Blade cleaning involves a blade, normally made of a rubberlike material (e.g. polyurethane) which is dragged or wiped across the surface to remove the residual particles from the surface. Blade cleaning is a highly desirable method, compared to other methods (e.g. brushes and webs), for removing residual particles due to its simple, inexpensive structure. To assure reliable and effective cleaning of the imaging surface, a certain amount of force must of necessity be applied to the blade to maintain the cleaning edge against the imaging surface with sufficient pressure to avoid allowing any particulate material on the imaging surface to slip past.
However, during periods when the machine is not in use and the imaging surface is stationary, the sustained pressure of the cleaning blade against a single point on the imaging surface can cause cold flow or crystallization of the imaging surface. When this happens, replacement or refurbishing of the imaging surface is usually necessary.
Many copying machines currently use a solenoid to engage and retract the cleaner blade from the photoreceptor. The solenoid to weight gap [i.e. the distance between the weight and the end of the solenoid plunger which is measured/adjusted when the solenoid is energized (The gap is present to allow the solenoid to achieve the momentum to overcome the spring force of the solenoid.)] adjustment is a set up procedure that needs to be performed in order for the solenoid to energize and allow the cleaner blade to come in contact with the photoreceptor. Data has been compiled from field reports on machines that utilize a solenoid and the frequency at which this adjustment must be made.
Another problem encountered is that the cleaning edge of the blade retains a certain amount of toner and/or residual particles after cleaning the imaging surface. When a blade containing these particles is reengaged with the imaging surface after retraction, these particles often fall onto the imaging surface due to the amount of force used to put the blade edge back in contact with the imaging surface. As a result, the photoreceptor transfers this defect onto the copy called a first copy reprint (FCR).
The following disclosures may be relevant to various aspects of the present invention and may be briefly summarized as follows:
U.S. Pat. No. 4,796,057 to Howard et al. discloses an apparatus for separating residual toner material from the surface of a reusable photoreceptor in a reproducing machine having a cleaner blade assembly. The cleaner blade assembly is movable between two positions. In a first position the blade operatively engages the photoreceptor to clean off the residual toner material which is then collected in a generally enclosed chamber below. In the second position the blade assembly is spaced apart form the photoreceptor but covers the entrance to the chamber forming a sealed enclosure for the contents. Thus, the toner collecting chamber is sealed by the cleaner blade alone without relying on the photoreceptor to perform a sealing function.
U.S. Pat. No. 4,639,122 to Pease discloses disengaging the cleaning blade from the photoreceptor of a reproduction machine to avoid cold set and damage to the photoreceptor during prolonged machine shutdowns. A bi-metal coil spring is positioned inside the fusing roll to sense fuser temperatures. A linkage couples the spring to the cleaning blade so that when fuser temperatures fall below a preset operating temperature, the spring relaxes permitting a weighted member to retract and disengage the blade from the photoreceptor.